var foo = function() {}; bar(function(){ baz(function() { qux(foo); }) }); //options: [2]
fn(function(){}, function(){}, function(){});     //options: [2]
fn(() => {}, function(){}, function(){});       // options: [2],
foo(function() {})
foo(function() { bar(thing, function(data) {}); });

foo1(handleFoo1);

function handleFoo1() {
  foo2(handleFoo2);
}

function handleFoo2() {
  foo3(handleFoo3);
}

function handleFoo3() {
  foo4(handleFoo4);
}

function handleFoo4() {
  foo5();
}